EP3747715A1 - Vehicle attitude control system - Google Patents

Vehicle attitude control system Download PDF

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Publication number
EP3747715A1
EP3747715A1 EP20176232.5A EP20176232A EP3747715A1 EP 3747715 A1 EP3747715 A1 EP 3747715A1 EP 20176232 A EP20176232 A EP 20176232A EP 3747715 A1 EP3747715 A1 EP 3747715A1
Authority
EP
European Patent Office
Prior art keywords
vehicle
road wheel
braking force
attitude control
turning
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP20176232.5A
Other languages
German (de)
English (en)
French (fr)
Inventor
Naoki Hiraga
Daisuke Umetsu
Fuminori Kato
Hiroyuki Ogata
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Mazda Motor Corp
Original Assignee
Mazda Motor Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mazda Motor Corp filed Critical Mazda Motor Corp
Publication of EP3747715A1 publication Critical patent/EP3747715A1/en
Withdrawn legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
    • B60T8/17—Using electrical or electronic regulation means to control braking
    • B60T8/1755—Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve
    • B60T8/17554—Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve specially adapted for enhancing stability around the vehicles longitudinal axle, i.e. roll-over prevention
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
    • B60W30/02—Control of vehicle driving stability
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
    • B60T8/17—Using electrical or electronic regulation means to control braking
    • B60T8/1755—Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve
    • B60T8/17555—Brake regulation specially adapted to control the stability of the vehicle, e.g. taking into account yaw rate or transverse acceleration in a curve specially adapted for enhancing driver or passenger comfort, e.g. soft intervention or pre-actuation strategies
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W10/00—Conjoint control of vehicle sub-units of different type or different function
    • B60W10/18—Conjoint control of vehicle sub-units of different type or different function including control of braking systems
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W10/00—Conjoint control of vehicle sub-units of different type or different function
    • B60W10/20—Conjoint control of vehicle sub-units of different type or different function including control of steering systems
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
    • B60W30/02—Control of vehicle driving stability
    • B60W30/025—Control of vehicle driving stability related to comfort of drivers or passengers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
    • B60W30/02—Control of vehicle driving stability
    • B60W30/04—Control of vehicle driving stability related to roll-over prevention
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
    • B60W30/02—Control of vehicle driving stability
    • B60W30/045—Improving turning performance
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
    • B60W30/18—Propelling the vehicle
    • B60W30/18172—Preventing, or responsive to skidding of wheels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W40/00—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models
    • B60W40/10—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models related to vehicle motion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W40/00—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models
    • B60W40/10—Estimation or calculation of non-directly measurable driving parameters for road vehicle drive control systems not related to the control of a particular sub unit, e.g. by using mathematical models related to vehicle motion
    • B60W40/11—Pitch movement
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T2201/00—Particular use of vehicle brake systems; Special systems using also the brakes; Special software modules within the brake system controller
    • B60T2201/16—Curve braking control, e.g. turn control within ABS control algorithm
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T2240/00—Monitoring, detecting wheel/tire behaviour; counteracting thereof
    • B60T2240/06—Wheel load; Wheel lift
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2520/00—Input parameters relating to overall vehicle dynamics
    • B60W2520/10—Longitudinal speed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2520/00—Input parameters relating to overall vehicle dynamics
    • B60W2520/12—Lateral speed
    • B60W2520/125—Lateral acceleration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2520/00—Input parameters relating to overall vehicle dynamics
    • B60W2520/28—Wheel speed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2540/00—Input parameters relating to occupants
    • B60W2540/10—Accelerator pedal position
    • B60W2540/106—Rate of change
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2540/00—Input parameters relating to occupants
    • B60W2540/18—Steering angle

Definitions

  • the present invention relates to a vehicle attitude control system, and more particularly to a vehicle attitude control system for controlling the attitude of a vehicle in which a road wheel suspension is configured such that a roll axis of a vehicle body inclines downwardly in a forward direction.
  • Patent Document 1 JP 5193885B (Patent Document 1), there is described a vehicle motion control device.
  • This vehicle motion control device is configured to apply different braking or driving forces, respectively, to right and left road wheels of a vehicle, based on a yaw moment control instruction value calculated from information about skid of the vehicle.
  • the invention described in the Patent Document 1 makes it possible to automatically perform acceleration/deceleration of the vehicle in connection with steering wheel manipulation, thereby reducing a skid in a critical driving range to improve safety performance.
  • the invention described in the Patent Document 1 intends to apply different braking or driving forces, respectively, to the right and left road wheels, in accordance with steering wheel manipulation by a driver, to apply a yaw moment directly to the vehicle, thereby controlling a yaw motion of the vehicle.
  • the attitude of a vehicle during turning it is also attempted to improve this property based on setting of basic specifications of suspensions of the vehicle. That is, it is also studied to set the basic specifications of the suspensions such that the vehicle is more likely to undergo a pitching motion, thereby making it possible to naturally produce an appropriate diagonal rolling motion in a vehicle body of the vehicle, even during turning with a low lateral acceleration. More specifically, the basic specifications of the suspensions of the vehicle are set such that a roll axis of the vehicle body inclines downwardly in a forward direction (a front end of the vehicle body is sunk down), so that the vehicle body becomes more likely to undergo a pitching motion, thereby making it possible to produce an appropriate diagonal rolling motion during turning.
  • Patent Document 1 JP 5193885B
  • the inner rear portion of the vehicle body being turning can be lifted up, even in the range in which the lateral acceleration is not really high, so that there is a possibility of giving a driver or passenger a feeling of insecurity.
  • the present invention provides a vehicle attitude control system for controlling an attitude of a vehicle having front and rear road wheels in which a road wheel suspension is configured such that a roll axis of the vehicle inclines downwardly in a forward direction.
  • the vehicle attitude control system comprises: a road wheel speed sensor configured to detect a road wheel speed of each road wheel of the vehicle; a brake actuator configured to apply a braking force to each road wheel of the vehicle; and a brake control device configured to send a control signal to the brake actuator to cause the brake actuator to generate the braking force based on a detection signal of the road wheel speed sensor, wherein the brake control device is configured to execute vehicle attitude control of applying a first braking force to the inner rear road wheel, the vehicle attitude control is executed during turning of the vehicle based on turning manipulation of a steering wheel of the vehicle, and the first braking force is applied based on a difference in road wheel speed between an inner rear road wheel and an outer rear road wheel of the vehicle being turning.
  • a pitching motion is easily induced, so that it is possible to produce a diagonal rolling motion even during turning of the vehicle with a low lateral acceleration, thereby improving turning performance.
  • the roll axis is inclined downwardly in the forward direction, when the lateral acceleration is increased to some degree, there arises a specific technical problem that an inner rear portion of the vehicle body tends to be lifted up, thereby giving a driver or passenger a feeling of insecurity.
  • the present invention is intended to solve the technical problem specific to the type of vehicle in which the roll axis of the vehicle body is inclined downwardly in the forward direction.
  • the vehicle attitude control system of the present invention having the above feature is configured to, during turning of the vehicle based on turning manipulation of a steering wheel of the vehicle, execute the vehicle attitude control of, based on a difference in road wheel speed between an inner rear road wheel and an outer rear road wheel of the vehicle being turning, applying a first braking force to the inner rear road wheel.
  • a force acts on the vehicle body through the road wheel suspension to pull the inner rear portion of the vehicle body downwardly, so that it is possible to suppress uplift of the inner rear portion of the vehicle body.
  • the first braking force to be applied to the inner rear road wheel is not at a level enough to substantially exert an influence on the turning performance of the vehicle, but acts to suppress uplift of the inner rear portion of the vehicle, thereby making it less likely to give a driver or passenger a feeling of insecurity.
  • the brake control device is configured to apply the first braking force to the inner rear road wheel, when the difference in road wheel speed between the inner rear road wheel and the outer rear road wheel of the vehicle occurs during the turning of the vehicle and, after the application of the first braking force, the brake control device is configured to maintain a braking force equal to or greater than a given lower limit braking force until the turning is completed, even when the difference in road wheel speed between the inner rear road wheel and the outer rear road wheel becomes smaller.
  • the first braking force is applied to the inner rear road wheel based on the road wheel speed difference between the inner and outer rear road wheels, and, after the application of the first braking force, a braking force equal to or greater than the lower limit braking force is maintained until the turning is completed, even when the road wheel speed difference becomes smaller, so that it is possible to suppress a situation where the braking force based on the vehicle attitude control sudden changes, thereby giving a driver a feeling of strangeness.
  • the brake control device is configured to apply a second braking force to the inner rear road wheel, when the road wheel speed of the inner rear road wheel of the vehicle becomes greater than the road wheel speed of the outer rear road wheel of the vehicle, during the turning of the vehicle.
  • the brake control device is configured to calculate each of the first braking force, the lower limit braking force, and the second braking force, based on the difference in road wheel speed between the inner rear road wheel and the outer rear road wheel of the vehicle being turning, and the brake control device is configured to control the brake actuator to apply a largest braking force among the first braking force, the lower limit braking force, and the second braking force.
  • the brake actuator is controlled to apply the largest braking force among the first braking force, the lower limit braking force, and the second braking force, so that it is possible to suppress interference among controls for applying a braking force for respective different purposes.
  • the brake control device is configured to be capable of selecting a low road surface friction mode or a high road surface friction mode, and to set the lower limit braking force, when the low road surface friction mode is selected.
  • the lower limit braking force is applied for the purpose of suppressing a large change in braking force at a time when the application of the second braking force is started after completion of the application of the first braking force.
  • the application of the second braking force is unlikely to be executed.
  • the lower limit braking force is set, so that it is possible to suppress a situation where the lower limit braking force is applied in the high road surface friction mode in which the lower limit braking force is unnecessary, thereby giving a driver a feeling of strangeness.
  • the above vehicle attitude control system comprises a friction coefficient estimation part to estimate a friction coefficient of a road surface on which the vehicle is traveling, wherein the brake control device is configured to set the low road surface friction mode or the high road surface friction mode, based on the friction coefficient of the road surface estimated by the friction coefficient estimation part, and, when the low road surface friction mode is set, the lower limit braking force is set.
  • the low road surface friction mode or the high road surface friction mode is set based on the friction coefficient of the road surface estimated by the friction coefficient estimation part, so that it is possible to suppress a situation where, due to negligence of the setting of the road surface friction mode, non-optimal vehicle attitude control is executed, a feeling of strangeness is given to a driver.
  • the road wheel suspension comprises a link mechanism which suspends an axle portion of each rear road wheel with respect to a vehicle body of the vehicle, wherein the link mechanism suspends the axle portion such that the axle portion is swingable about a given suspension center, and wherein the suspension center is located above the axle portion.
  • the link mechanism suspends the axle portion of each rear road wheel with respect to the vehicle body, such that the axle portion is swingable about a given suspension center. Further, the suspension center is located above the axle portion.
  • the vehicle attitude control system of the present invention is capable of, even if it used in a vehicle in which a suspension is set such that a roll axis of a vehicle body inclines downwardly in a forward direction, suppressing uplift of an inner rear portion of the vehicle body during turning.
  • FIG. 1 is a layout diagram showing the overall configuration of the vehicle equipped with the vehicle attitude control system according to this embodiment.
  • the reference sign 1 denotes the vehicle equipped with the vehicle attitude control system according to this embodiment.
  • left and right front road wheels 2a, 2b as steerable road wheels are provided in a front portion of a vehicle body 1a thereof, and left and right rear road wheels 2c, 2d as drive road wheels are provided in a rear portion of the vehicle body.
  • Each of the front road wheels 2a, 2b and the rear road wheels 2c, 2d is supported by a suspension unit 3 constituting a road wheel suspension.
  • the vehicle 1 comprises an engine 4 mounted to the front portion of the vehicle body 1a to serve as a prime mover for driving the rear road wheels 2c, 2d.
  • the engine 4 is a gasoline engine.
  • the vehicle 1 is a so-called FR vehicle in which the rear road wheels 2c, 2d are driven by the engine 4 mounted to the front portion of the vehicle body 1a via a transmission 4a, a propeller shaft 4b and a differential gear unit 4c.
  • the present invention can be applied to a vehicle having any other drive system, such as a so-called RR vehicle in which rear road wheels are driven by an engine mounted to a rear portion of a vehicle body thereof, or a so-called FF vehicle in which front road wheels are driven by an engine mounted to a front portion of a vehicle body thereof
  • the vehicle 1 is equipped with a steering device 7 for steering the front road wheels 2a, 2b in accordance with turning/turning-back manipulation of a steering wheel 6.
  • the vehicle 1 comprises a brake control system for supplying a brake hydraulic pressure to a wheel cylinder or a brake caliper (not shown) of a brake unit (in-wheel brake unit) 8 serving as a brake actuator installed in each of the road wheels.
  • the brake control system also comprises a hydraulic pump 10 for producing a brake hydraulic pressure necessary for generating a braking force in each of the in-wheel brake units 8.
  • the hydraulic pump 10 is configured to be driven by electric power supplied from, e.g., a battery (not shown), so as to produce a brake hydraulic pressure necessary for generating a braking force in each of the in-wheel brake units 8, even in a state in which a brake pedal (not shown) is not depressed.
  • the brake control system comprises four valve units 12 (specifically, solenoid valves) each provided in a respective one of four hydraulic pressure supply lines connected, respectively, to the in-wheel brake units 8, and each configured to control a hydraulic pressure to be supplied from the hydraulic pump 10 to a corresponding one of the in-wheel brake units 8.
  • the degree of valve opening of each of the valve units 12 is changed by adjusting an electric power supply amount from the battery to the valve unit 12.
  • the brake control system comprises four hydraulic pressure sensors 13 each for detecting a hydraulic pressure to be supplied from the hydraulic pump 10 to a respective one of the in-wheel brake units 8.
  • Each of the hydraulic pressure sensors 13 is disposed, e.g., at a connection between a respective one of the valve units 12 and a portion of the hydraulic pressure supply line on a downstream side of the valve unit 12, and configured to detect a hydraulic pressure at a position just downstream of the valve unit 12 and output a detection value to a power-train control module (PCM) 14.
  • PCM power-train control module
  • the brake control system is operable, based on a braking force instruction value and detection values of the hydraulic pressure sensors 13 input from the PCM 14, to calculate hydraulic pressures to be independently supplied, respectively, to the wheel cylinders or brake calipers in the road wheels, and control a pump speed of the hydraulic pump 10 and respective value opening degrees of the valve units 12.
  • FIG. 2 is a schematic diagram showing a structure for suspending an axle portion of each of the rear road wheels 2c, 2d with respect to the vehicle body 1a of the vehicle 1, when viewed from behind the vehicle 1.
  • FIG. 3 is a schematic diagram showing a roll axis of the vehicle body of the vehicle equipped with the vehicle attitude control system according to this embodiment.
  • FIG. 4 is a schematic explanatory diagram of a force acting on the vehicle body when a braking force is applied to the rear road wheels of the vehicle.
  • an axle portion 2e of the left rear road wheel 2c of the vehicle 1 is supported by the suspension unit 3 with respect to the vehicle body 1a of the vehicle 1a.
  • the axle portion 2e of the rear road wheel 2c is supported by an upper arm 3a and a lower arm 3b which constitute a link mechanism of the suspension unit 3.
  • Respective extended lines of the upper arm 3a and the lower arm 3b each connecting the rear road wheel 2c and the vehicle body 1a together intersect at an intersection point P 1 .
  • a straight line connecting the intersection point P 1 and a ground contact point P 2 of the rear road wheel 2c intersects with a central axis A of the vehicle body 1a at a point P rR (the central axis A corresponds to an upward-downward directional plane including a longitudinal central axis of the vehicle body 1a).
  • This point P rR is the center of rolling motion (roll center) in the rear portion of the vehicle body 1a, i.e., the rear portion of the vehicle body 1a undergoes the rolling motion about point P rR .
  • the vehicle 1 is bilaterally symmetric.
  • the center P rR is determined as the center of the rolling motion.
  • the center P rF of the rolling motion can be determined in the same manner.
  • FIG. 3 is a schematic diagram showing respective projected points of the center P rR of the rolling motion in the rear portion of the vehicle body 1a, and the center P rF of the rolling motion in the front portion of the vehicle body 1a, when viewed laterally inwardly from outside the vehicle 1.
  • An axis A r connecting the center P rR of the rolling motion in the rear portion of the vehicle body 1a and the center P rF of the rolling motion in the front portion of the vehicle body 1a is defined as a central axis during the rolling motion of the vehicle body 1a.
  • the vehicle body 1a of the vehicle 1 undergoes the rolling motion about the roll axis A r .
  • the roll axis A r of the vehicle 1 inclines downwardly in a forward direction of the vehicle, i.e., inclined such that a front end of the vehicle 1 is sunk down, as shown in FIG. 3 .
  • the roll axis A r of the vehicle 1 is set to incline downwardly in the forward direction, so that it is possible to naturally produce an appropriate diagonal rolling motion during turning of the vehicle 1, thereby improving turning performance of the vehicle 1.
  • each of the rear road wheels 2c, 2d is suspended by the upper arm 3a and the lower arm 3b constituting the suspension unit 3.
  • a road wheel is likely to be suspended by various types of suspensions.
  • an axle portion of the road wheel can be deemed to be suspended such that the axle portion is swingable about a given virtual suspension center.
  • the rear road wheel 2d is suspended such that the rear road wheel 2d is swingable about a suspension center Ps, as shown in FIG. 4 .
  • this suspension center P S is located above the axle portion 2e of the rear road wheel 2d.
  • a force component pulling the vehicle body 1a downwardly can be calculated as follows: F x ⁇ tan ⁇ al .
  • a moment M a1 pulling the rear portion of the vehicle body 1a downwardly can be calculated by the following formula (1).
  • M al l r ⁇ X r ⁇ F x ⁇ tan ⁇ al
  • the suspension center P S is located at a position higher than that of the axle portion 2e of the rear road wheel, so that the force pulling the vehicle body 1a downwardly becomes relatively large.
  • FIG. 5 is a block diagram showing the PCM, sensors connected to the PCM, etc., equipped in the vehicle 1
  • the vehicle 1 is equipped with: a steering angle sensor 16 for detecting a turning angle of the steering wheel 6 (steering angle); an accelerator position sensor 18 for detecting a depression amount (relative position) of an accelerator pedal; and a vehicle speed sensor 20 for detecting a vehicle speed. Detection signals from these sensors are input to the PCM 14. Further, the vehicle 1 is equipped with: a lateral acceleration sensor 22 for detecting a lateral acceleration acting on the vehicle 1; four road wheel speed sensors 24 each for detecting a road wheel speed of a respective one of the road wheels of the vehicle 1; and the hydraulic pressure sensors 13 each for detecting the hydraulic pressure on the downstream side of a respective one of the valve units 12 ( FIG. 1 ).
  • Detection signals from these sensors are also input to the PCM 14.
  • a sensor configured to directly measure the lateral acceleration is equipped in the vehicle 1.
  • the sensor configured to directly measure the lateral acceleration needs not necessarily be used as the lateral acceleration sensor 22, but the lateral acceleration may be calculated from a detection value measured by another sensor.
  • the term "lateral acceleration sensor” includes any sensor usable for determining the lateral acceleration.
  • the vehicle 1 is configured to allow a driver to select a low road surface friction mode or a high road surface friction mode, in conformity to a state of a road surface on which the vehicle of the driver is traveling, and provided with a mode setting switch 26 for selecting one of the modes.
  • a mode setting switch 26 for selecting one of the modes.
  • this setting is input to the PCM 14 to execute vehicle attitude control in conformity to the road surface state, as described later.
  • the PCM 14 internally comprises: a brake control part 14a to control the brake units 8 to serve as a brake control device; a turning control part 14b to execute turning control for improving the turning performance of the vehicle 1; and an anti-skid control part 14c to execute anti-skid control for suppressing a skid during turning of the vehicle 1.
  • Each of the control parts 14a, 14b, 14c is configured to send a control signal to the engine 4 or the brake units 8 to execute a corresponding one of the vehicle attitude control, the turning control and the anti-skid control.
  • the vehicle attitude control system comprises: the steering angle sensor 16, the accelerator position sensor 18, the vehicle speed sensor 20, the lateral acceleration sensor 22, the road wheel speed sensor 24 and the mode setting switch 26 each sending a signal to the PCM 14; the brake control part 14a, the turning control part 14b and the anti-skid control part 14c each internally comprised in the PCM 14; and the engine 4 and the brake units 8 to be controlled by the PCM 14. It should be noted here that the above elements constituting the vehicle attitude control system may be partly omitted according to an intended application.
  • the control parts of the PCM 14 are composed of a computer which comprises: a CPU; various programs (including a basic control program such as an OS, and an application program capable of being activated on the OS to realize a specific function) to be interpreted and executed by the CPU; and an internal memory such as a ROM or a RAM for storing therein the programs and a variety of data (the above components are not shown in the figures).
  • various programs including a basic control program such as an OS, and an application program capable of being activated on the OS to realize a specific function
  • an internal memory such as a ROM or a RAM for storing therein the programs and a variety of data (the above components are not shown in the figures).
  • FIG. 6 is a flowchart showing the operation of the vehicle attitude control system.
  • FIG. 7 is a flowchart of a subroutine to be called from the flowchart illustrated in FIG. 6 .
  • FIG. 8 is a time chart showing the operation of the vehicle attitude control system during traveling on a normal road surface.
  • FIG. 9 is a time chart showing the operation of the vehicle attitude control system during traveling on a road surface having a low friction coefficient.
  • FIGS. 10 to 18 are maps for use in setting a vehicle attitude control instruction value in the vehicle attitude control system.
  • the flowchart illustrated in FIG. 6 is repeatedly executed mainly in the PCM 14 at given time intervals, so as to automatically apply a braking force to the vehicle 1.
  • step S1 of FIG. 6 detection signals of various sensors are read from the sensors into the PCM 14.
  • the detection signals read in the step S1 are used in processings in steps S2 to S4.
  • a signal of the steering angle (turning angle of the steering wheel) [deg] from the steering angle sensor 16 a signal of the accelerator position [%] from the accelerator position sensor 18, and a signal of the vehicle speed [km/h] from the vehicle speed sensor 20, are read.
  • a signal of the lateral acceleration [G] from the lateral acceleration sensor 22, a signal of the road wheel speed [m/sec] from each of the road wheel speed sensors 24 and a signal of the brake hydraulic pressure [MPa] from each of the hydraulic pressure sensors 13 are read. Further, a selection signal indicative of which of the low road surface friction mode and the high road surface friction mode is currently selected by a driver is read from the mode setting switch 26.
  • step S2 processing of setting an instruction value for the vehicle attitude control is executed. Specifically, during turning of the vehicle 1 based on turning manipulation of the steering wheel 6 of the vehicle 1, as the vehicle attitude control, a braking force is applied to an inner rear road wheel of the vehicle 1 being turning, so as to suppress uplift of an inner rear portion of the vehicle body 1a of the vehicle being turning. For example, in FIG. 1 , when the vehicle 1 turns leftwardly, a braking force is applied to the left rear road wheel 2c, thereby suppressing uplift of a left rear portion of the vehicle body 1a.
  • This vehicle attitude control is executed in a range in which the lateral acceleration during turning of the vehicle 1 is relatively low, and is configured to apply a relatively small first braking force to the inner rear road wheel, based on a difference in road wheel speed between the inner rear road wheel and an outer rear road wheel.
  • a braking force to be applied to the vehicle 1 having a mass of about 960 kg to about 1060 kg for the purpose of the vehicle attitude control is produced by applying a hydraulic pressure of 0.02 MPa to 0.1 MPa from the hydraulic pump 10 to the brake unit 8 of the inner rear road wheel.
  • a hydraulic pressure of 0.02 MPa to 0.1 MPa from the hydraulic pump 10 to the brake unit 8 of the inner rear road wheel.
  • step S3 processing of setting an instruction value for the turning control is executed.
  • the turning control is intended to improve the turning performance of the vehicle 1, and is executed by the turning control part 14b of the PCM 14 when a steering angular speed of the steering wheel 6 becomes equal to or greater than a given value.
  • the turning control is configured to adjust a torque to be generated by the engine 4, and/or apply a braking force to the vehicle 1 by the brake unit 8. Specifically, in the case where a braking force is to the vehicle 1 during the turning control, a braking force is applied to the inner rear road wheel of the vehicle 1 being turning, thereby generating a yaw moment in a turning direction of the vehicle 1 to improve the turning performance of the vehicle 1.
  • a braking force is also applied to the inner rear road wheel of the vehicle 1 being turning.
  • the turning control is intended to be executed in a range in which the lateral acceleration is relatively high as compared to that in the vehicle attitude control, and is configured to apply a larger braking force than that in the vehicle attitude control, to the vehicle 1. That is, the vehicle attitude control is completely different from the turning control, in that the vehicle attitude control is executed for the purpose of suppressing the uplift of the inner rear portion of the vehicle body 1a during turning of the vehicle 1, whereas the turning control is executed for the purpose of applying the yaw moment to the vehicle 1 to improve the turning performance.
  • a braking force to be applied for the turning control is generated by applying a hydraulic pressure of 0.2 MPa to 0.5 MPa, which is greater than that for the vehicle attitude control, from the hydraulic pump 10 to the brake unit 8 of the inner rear road wheel.
  • step S4 processing of setting an instruction value for the anti-skid control is executed.
  • the anti-skid control is control to be executed by the anti-skid control part 14c of the PCM 14 for the purpose of suppressing or preventing a situation where the vehicle 1 skids during turning.
  • This anti-skid control is control to be executed based on the steering angle of the steering wheel 6, and the lateral acceleration of the vehicle 1, and executed in a range in which the lateral acceleration is significantly greater than that in the turning control.
  • an appropriate braking force is applied to each of the road wheels of the vehicle 1.
  • a braking force to be applied in the anti-skid control is set to be significantly greater than that in the turning control.
  • a braking force to be applied for the anti-skid control is generated by applying a hydraulic pressure of 20 MPa or more, which is greater than that for the turning control, from the hydraulic pump 10 to each of the brake units 8.
  • step S5 a control signal based on the instruction value set in one of the steps S2 to S4 is transmitted to the brake unit(s) 8 to apply a braking force to the vehicle 1, and then one cycle of the processing routine of the flowchart illustrated in FIG. 6 is completed.
  • the vehicle attitude control, the turning control and the anti-skid control are executed, respectively, in different traveling states, and thereby not normally executed in an overlapped manner, although all the controls are configured to apply a braking force to the vehicle 1.
  • FIG. 7 is a subroutine to be called from the step S2 of the flowchart in FIG. 6 , and executed by the brake control part 14a of the PCM 14.
  • FIGS. 8 and 9 are time charts each showing an example of a braking force generated when the vehicle attitude control is executed.
  • FIG. 8 shows a time chart in a state in which the vehicle 1 is traveling on a normal road surface (high friction road surface)
  • FIG. 9 shows a time chart in a state in which the vehicle 1 is traveling on a low friction road surface.
  • FIGS. 8 shows a time chart in a state in which the vehicle 1 is traveling on a normal road surface (high friction road surface)
  • FIG. 9 shows a time chart in a state in which the vehicle 1 is traveling on a low friction road surface.
  • the horizontal axis represents time
  • the vertical axis represents a detection value of the steering angle sensor 16, a detection value of the accelerator position sensor 18, the road wheel speed of the rear road wheel detected by the road wheel speed sensors 24, and a control instruction value for a braking force to be applied to the inner rear road wheel, which are arranged in this order from top down.
  • step S11 in FIG. 7 a difference in road wheel speed between the left and right rear road wheels 2c, 2d of the vehicle 1 is calculated. Specifically, the road wheel speed difference between the left and right rear road wheels 2c, 2d is calculated based on respective road wheel speeds of the road wheels read from the road wheel speed sensors 24 in the step S1 of FIG. 6 .
  • step S12 it is determined whether or not a "vehicle attitude control flag” is “True”.
  • the “vehicle attitude control flag” is a flag configured to be changed to “True” when the vehicle 1 starts turning, and the vehicle attitude control is stated based on a given condition and to be returned to "False” when the steering wheel 6 in a turned state is turned back, and the turning is completed.
  • the vehicle attitude control flag is "False"
  • the processing subroutine of the flowchart in FIG. 7 proceeds to step S16.
  • step S16 the inner rear road wheel and the outer rear road wheel of the vehicle being turning are compared in terms of the road wheel speed.
  • the processing subroutine proceeds to step S17.
  • the processing subroutine proceeds to step S21.
  • the road wheel speed of the outer rear road wheel is greater than that of the inner rear road wheel.
  • this relationship is reversed when a certain level of slip occurs in the inner rear road wheel. In the example illustrated in FIG.
  • step S17 it is determined whether or not the road wheel speed difference between the outer rear road wheel and the inner rear road wheel (the outer rear road wheel speed - the inner rear road wheel speed) is greater than a first road wheel speed difference threshold T a [m/sec] which is a threshold of the road wheel speed difference.
  • first road wheel speed difference threshold T a [m/sec] which is a threshold of the road wheel speed difference.
  • the vehicle attitude control is permitted to intervene, under the condition of a small road wheel speed difference, there is a possibility of giving a driver a feeling of strangeness. Therefore, in a situation where the road wheel speed difference is small, the vehicle attitude control is not executed.
  • the first road wheel speed difference threshold T a [m/sec] which is a threshold of the road wheel speed difference is changed according to the vehicle speed of the vehicle 1. Setting of a specific value of the first road wheel speed difference threshold will be described later with reference to FIG. 10 .
  • step S18 when the driver performs the turning manipulation of the steering wheel 6 at the time t 1 to cause the vehicle 1 to start turning, the road wheel speed difference gradually increases. Then, when the road wheel speed difference exceeds the road wheel speed difference T a , processings in step S18 and subsequent steps will be executed.
  • Va first vehicle speed threshold
  • the processings of the step S23 and the subsequent steps are executed, and then one cycle of the processing subroutine of the flowchart illustrated in FIG. 7 is completed without performing the application of the first braking force based on the vehicle attitude control.
  • the vehicle attitude control is not executed.
  • the processings of the step S19 and the subsequent steps are executed to apply the first braking force based on the vehicle attitude control.
  • the vehicle attitude control flag is changed to "True".
  • the processing subroutine of the flowchart in FIG. 7 proceeds from the step S12 to the step S13.
  • the high road surface friction mode is set through the mode setting switch 26.
  • the processing subroutine of the flowchart illustrated in FIG. 7 proceeds from the step S13 to the step S16, so that processings of steps S14 and S15 are not executed.
  • a basic instruction value F b1 [N] for the vehicle attitude control is set based on the road wheel speed difference between the left and right rear road wheels. Specifically, a braking force to be applied to the inner rear road wheel of the vehicle 1 being turning, based on the road wheel speed difference between the inner and outer rear road wheels.
  • This basic instruction value F b1 is an instruction value of a braking force to be applied to the inner rear road wheel of the vehicle 1 being turning, and is calculated by multiplying a difference between an outer road wheel speed V o and an inner road wheel speed V i by a given coefficient C m1 , as expressed in the following formula (2).
  • F b 1 C m 1 ⁇ V o ⁇ V i
  • step S25 the basic instruction value F b1 calculated in the step S20 is multiplied by various gains, thereby setting a final instruction value F 1 for the vehicle attitude control. Specific processing to be executed in the step S25 will be described later.
  • step S26 instruction values calculated for various controls are compared with each other, and a largest one of the instruction values is selected as a final instruction value.
  • a lower limit braking force based on pre-brake limited slip differential (pre-brake LSD) control, and a second braking force based on brake limited slip differential (brake LSD) control are calculated, respectively, in the step S15 and step S22, as mentioned later.
  • pre-brake LSD pre-brake limited slip differential
  • brake LSD brake limited slip differential
  • the vehicle 1 enters a steady turning state. Accordingly, the road wheel speed in each of the inner and outer rear road wheels gradually rises, and the road wheel speed difference between the inner and outer rear road wheels gradually decreases (time t 3 to time t 4 in FIG. 8 ). Therefore, the basic braking force instruction value calculated by the formula (2) also gradually decreases. Then, at the time t 4 in FIG. 8 , the road wheel speed difference between the inner and outer rear road wheels becomes equal to or less than the first road wheel speed difference threshold T a . Thus, the processing subroutine of the flowchart in FIG. 7 proceeds from the step S17 to the step S23, so that the instruction value for the vehicle attitude control becomes zero.
  • step S21 it is determined whether or not the road wheel speed difference between the inner rear road wheel and the outer rear road wheel (the inner rear road wheel speed - the outer rear road wheel speed) is greater than a second road wheel speed difference threshold T b [m/sec].
  • a second road wheel speed difference threshold T b [m/sec].
  • the brake LSD control is permitted to intervene, under the condition of a small road wheel speed difference, there is a possibility of giving a driver a feeling of strangeness. Therefore, in a situation where the road wheel speed difference is small, the brake LSD control is not executed.
  • the processing subroutine proceeds to the step S22, and, in the step S22, a basic instruction value of a second braking force for the brake LSD control is calculated.
  • the brake control part 14a is operable, when the road wheel speed of the inner rear road wheel of the vehicle 1 becomes greater than that of the outer rear road wheel of the vehicle 1, to apply the second braking force to the inner rear road wheel.
  • the brake LSD control is control of applying a brake to a road wheel being slipping to reduce the road wheel speed thereof, thereby avoiding such a slip state.
  • an inner drive wheel in this embodiment, the inner rear road wheel
  • the inner drive wheel starts slipping.
  • a driving force becomes unable to be transmitted to the outer rear road wheel via the differential gear unit 4c.
  • a braking force is applied to the inner rear road wheel to reduce the road wheel speed of the inner rear road wheel.
  • a basic instruction value F b2 [N] for the brake LSD control is set based on the road wheel speed difference between the left and right rear road wheels.
  • This basic instruction value F b2 of the second braking force for the brake LSD control is an instruction value of a braking force to be applied to the inner rear road wheel of the vehicle 1 being turning, and is calculated by multiplying a difference between the inner road wheel speed V i and the outer road wheel speed V o by a given coefficient C m2 , as expressed in the following formula (3).
  • F b 2 C m 2 ⁇ V i ⁇ V o
  • the processing subroutine of the flowchart in FIG. 7 proceeds as follows: the step S16 ⁇ S21 ⁇ S23, or the step S16 ⁇ S17 ⁇ S23, so that no braking force is applied to the inner rear road wheel (time t 6 to time t 7 in FIG. 8 ).
  • the driver starts turning-back manipulation of the steering wheel 6 from the time t 6 , and completes the turning-back manipulation at the time t 7 , so that the turning of the vehicle 1 is completed to allow the vehicle 1 to travel straight ahead again.
  • step S23 it is determined, based on a detection value of the steering angle sensor 16, whether or not the turning-back manipulation of the steering wheel 6 has been completed.
  • the processing subroutine proceeds to the step S25.
  • the processing subroutine proceeds to step S24.
  • the brake control part 14a is operable to generate a braking force by a brake hydraulic pressure of about 0.1 MPa or less.
  • the "vehicle attitude control flag" is changed to "False” in the step S24. Subsequently, when the processing subroutine of the flowchart illustrated in FIG. 7 is executed, it will proceed from the step S12 to the step S16. As long as this state is continued, the lower limit braking force based on the pre-brake LSD control is never applied, even in a situation where the low road surface friction mode is set through the mode setting switch 26.
  • the time chart illustrated in FIG. 9 shows one example of the vehicle attitude control in the situation where the low road surface friction mode is set.
  • the time chart in FIG. 9 is different from the time chart in in FIG. 8 , in that, in the situation where the low road surface friction mode is set, processings of the step S14 and the subsequent steps are executed in the flowchart illustrated in FIG. 7 .
  • the lower limit braking force based on the pre-brake LSD control is calculated.
  • the instruction value for the vehicle attitude control is indicated by the solid line. Further, the instruction value for the pre-brake LSD control is indicated by the broken line
  • the low road surface friction mode and the high road surface friction mode are switched therebetween according to the manual setting of the mode setting switch 26 by the driver.
  • the vehicle attitude control system of the present invention may be configured such that the two modes are automatically switched therebetween, in addition to or instead of the manual setting of the mode setting switch 26.
  • the brake control part 14a may be configured to estimate a friction coefficient of a road surface, based on an outside air temperature sensor and/or a rainfall sensor installed in the vehicle 1, an operating state of a windshield wiper, a slip state of the drive road wheels, etc., and, when the estimated friction coefficient is equal to or less than a given value, automatically set the low road surface friction mode.
  • the brake control part 14a also functions as a friction coefficient estimation part to estimate a friction coefficient of a road surface on which the vehicle 1 is traveling.
  • step S13 it is determined whether or not the low road surface friction mode is set.
  • the low road surface friction mode is set, so that the processing subroutine proceeds to the step S14.
  • step S14 it is determined whether or not the lateral acceleration detected by the lateral acceleration sensor 22 is greater than a given second lateral acceleration threshold GY b [G].
  • the processing subroutine proceeds to the step S16 without applying the lower limit braking force based on the pre-brake LSD control.
  • the second lateral acceleration threshold GY b is set to a value less than the first lateral acceleration threshold GY a .
  • pre-brake LSD control is not executed.
  • the processing subroutine proceeds to the step S15.
  • a basic instruction value F b3 of the lower braking force for the pre-brake LSD control is set.
  • the basic instruction value F b3 is calculated by multiplying a maximum value of recently-set basic instruction values F b1 for the vehicle attitude control by a given coefficient C m3 , as expressed in the following formula (4).
  • F b 3 C m 3 ⁇ F b 1
  • the coefficient C m3 is set to a positive value less than 1. That is, the basic instruction value F b3 for the pre-brake LSD control is set to a value which is always less than a maximum one of recently-set basic instruction values F b1 for the vehicle attitude control.
  • the basic instruction value F b1 for the vehicle attitude control has a rising tendency, so that a maximum value thereof is also successively updated, and therefore the basic instruction value F b3 obtained by multiplying this maximum value by the coefficient C m3 also increases.
  • the basic instruction value F b1 for the vehicle attitude control becomes constant at its maximum value, i.e., the maximum value becomes a constant value, so that the basic instruction value F b3 obtained by multiplying this maximum value by the coefficient C m3 also becomes a constant value.
  • the maximum value of the basic instruction value F b1 is retained for further calculation, so that the basic instruction value F b3 obtained by multiplying this maximum value by the coefficient C m3 is maintained.
  • the basic instruction value F b3 for the pre-brake LSD control is maintained until the turning of the vehicle 1 is completed at time t 17 , and the vehicle attitude control flag is changed to "False" (step S23 ⁇ S24).
  • a braking force equal to or greater than the given lower limit braking force is maintained until turning of the vehicle 1 is completed, even when the road wheel speed difference between the inner and outer rear road wheels becomes smaller.
  • the lower limit braking force based on the pre-brake LSD control is applied for the purpose of suppressing the situation where, if the application of the second braking force based on the brake LSD control is started (at time t 15 in FIG. 9 ) after the application of the first braking force based on the vehicle attitude control is completed (at time t 14 in FIG. 9 ), the magnitude of braking force applied to the inner rear road wheel of the vehicle 1 varies in a short period of time, thereby giving the driver a feeling of strangeness.
  • the lower limit braking force for the pre-brake LSD control is set only in the situation where the low road surface friction mode is selected, and the pre-brake LSD control is not executed in the situation where the high road surface friction mode is selected (step S13 ⁇ S16 in FIG. 7 ).
  • the vehicle attitude control system of the present invention may be configured such that the pre-brake LSD control is executed even in the situation where the high road surface friction mode is selected.
  • the coefficient C m3 for the high road surface friction mode is preferably set to a value less than the coefficient C m3 for the low road surface friction mode.
  • the basic instruction value F b2 for the brake LSD control is set.
  • the basic instruction value F b1 for the vehicle attitude control is set.
  • the basic instruction value F b3 for the pre-brake LSD control is set, and, during a period between the time t 15 and the time t 16 , the basic instruction value F b2 for the brake LSD control is set.
  • step S25 a gain by which each of the basic instruction values is multiplied is set with respect to each of the basic instruction values, and each of three (final) instruction values F 1 , F 2 , F 3 is calculated by multiplying a respective one of the basic instruction values by the gain. Then, in the step S26, the instruction values F 1 , F 2 , F 3 are compared with each other to adopt a largest one of the instruction values, and a braking force corresponding to the largest instruction value is applied to the inner rear road wheel.
  • the setting of the gain by which each of the basic instruction values is multiplied in the step S25 will be described later with reference to FIGS. 11 to 18 .
  • FIG. 10 is one example of a map for setting the threshold of the road wheel speed difference.
  • a value of the first road wheel speed difference threshold T a [m/sec] in the step S17 illustrated in FIG. 7 is set based on the map illustrated in FIG. 10 .
  • the value of the first road wheel speed difference threshold T a is changed based on the vehicle speed of the vehicle 1 detected by the vehicle speed sensor 20.
  • the value of the first road wheel speed difference threshold T a is maximum at a vehicle speed of 0, and, after decreasing along with an increase in vehicle speed, becomes approximately constant after the vehicle speed becomes equal to or greater than a given vehicle speed value V 1 .
  • the given vehicle speed value V 1 is set to about 80 to about 100 [km/h]
  • the first road wheel speed difference threshold T a is set to become about 0.02 to about 0.05 [m/sec] at this value or more.
  • the vehicle attitude control By changing the threshold of the road wheel speed difference according to the vehicle speed in the above manner, it is possible to change a condition for starting the execution of the vehicle attitude control. Specifically, by setting the first road wheel speed difference threshold T a as the threshold of the road wheel speed difference in the above manner, the vehicle attitude control to be executed at the step S18 and the subsequent steps in FIG. 7 becomes less likely to intervene, in a low vehicle speed range. More specifically, in the low vehicle speed range, errors are more likely to occur in measurement value of the road wheel speed. Thus, if the vehicle attitude control is executed when the road wheel speed difference is small, the vehicle attitude control is likely to be executed in the presence of the measurement errors. With a view to suppressing such an unnecessary intervention of the vehicle attitude control, in this embodiment, the value of the first road wheel speed difference threshold T a is set as shown in FIG. 10 .
  • FIG. 11 is a map of a steering angle gain which is set based on the steering angle and by which the basic instruction value F b1 for the vehicle attitude control is multiplied.
  • FIGS. 12 to 14 are maps for use in a situation where the high road surface friction mode is set.
  • FIG. 12 is a map of an accelerator position gain which is set based on the accelerator position and by which the basic instruction value F b1 for the vehicle attitude control is multiplied.
  • FIG. 13 is a map of a lateral acceleration gain which is set based on the lateral acceleration and by which the basic instruction value F b1 for the vehicle attitude control is multiplied.
  • FIG. 14 is a map of a vehicle speed gain which is set based on the vehicle speed and by which the basic instruction value F b1 for the vehicle attitude control is multiplied.
  • FIGS. 15 to 17 are maps for use in a situation where the low road surface friction mode is set.
  • FIG. 15 is a map of an accelerator position gain which is set based on the accelerator position and by which the basic instruction value F b1 for the vehicle attitude control is to be multiplied.
  • FIG. 16 is a map of a lateral acceleration gain which is set based on the lateral acceleration and by which the basic instruction value F b1 for the vehicle attitude control is multiplied.
  • FIG. 17 is a map of a vehicle speed gain which is set based on the vehicle speed and by which the basic instruction value F b1 for the vehicle attitude control is multiplied.
  • FIG. 18 is a map of a rotation speed difference gain which is set based on the road wheel speed difference between the inner and outer rear road wheels and by which the basic instruction value Fb2 for the brake LSD control is multiplied
  • the steering angle gain G ⁇ is set such that it becomes zero in a range in which the steering angle ⁇ [deg] is equal to or less than a first steering angle value ⁇ 1 , and increases after the steering angle becomes greater than ⁇ 1 , whereafter it converges to "1" after the steering angle becomes equal to or greater than a given value.
  • the first steering angle value ⁇ 1 is set to about 3.5 to about 6.0 [deg]
  • the steering angle gain G ⁇ is set such that it becomes zero in the range in which the steering angle ⁇ [deg] is equal to or less than this value.
  • the accelerator position gain G aH is set such that it increases along with an increase in the accelerator position [%] to reach "1" at a first accelerator position value A 1 , and, after the accelerator position becomes greater than the first accelerator position value A 1 , converges to a given value greater than "1".
  • the accelerator position gain G aH in this manner, the final instruction value for the vehicle attitude control becomes smaller along with a decrease in the accelerator position. Specifically, in a range in which the acceleration position is small, uplift of the inner rear portion of the vehicle body 1a is less likely to occur.
  • the above setting makes it possible to suppress a situation where, due to unnecessary intervention of the vehicle attitude control in such a range, a feeling of strangeness is given to the driver.
  • the first accelerator position value A 1 is set to about 45 to about 60 [%], and the accelerator position gain G aH is set such that it becomes equal to less than "1" in a range in which the acceleration position is equal to or less than this value, and becomes greater than "1" in a range in which the acceleration position is greater than this value.
  • the lateral acceleration gain G 1H is set such that it becomes zero in a range in which the lateral acceleration a 1 [G] is equal to or less than a first lateral acceleration value an, and increases after the lateral acceleration becomes greater than an, whereafter it converges to "1" after the lateral acceleration becomes equal to or greater than a given value.
  • the first lateral acceleration value an is set to about 0.22 to about 0.35 [G]
  • the lateral acceleration gain G 1H is set such that it becomes zero in the range in which the lateral acceleration is equal to or less than this value.
  • the vehicle speed gain G VH is set such that it increases along with an increase in the vehicle speed [km/h] to reach "1" at a first vehicle speed value V 1 , and relatively rapidly increases after the vehicle speed becomes greater than first vehicle speed value V 1 .
  • the vehicle speed gain G VH in this manner, it is possible to apply, to the inner rear road wheel of the vehicle being turning, a larger braking force when the vehicle speed is relatively high than when the vehicle speed is relatively low.
  • uplift of the inner rear portion of the vehicle body 1a is less likely to occur.
  • the problem of uplift of the inner rear portion of the vehicle body 1a becomes more prominent along with an increase in the vehicle speed.
  • the final instruction value for the vehicle attitude control is increased to cause the vehicle attitude control to strongly intervene.
  • the first vehicle speed value V 1 is set to about 95 to about 115 [km/h]
  • the vehicle speed gain G VH is set such that it becomes equal to less than "1" in a range in which the vehicle speed is equal to or less than this value, and relatively rapidly increases in a range in which the vehicle speed is greater than this value.
  • the final instruction value F 1 for the vehicle attitude control is calculated by multiplying the basic instruction value F b1 for the vehicle attitude control by the steering angle gain G ⁇ set as shown in FIG. 11 , the accelerator position gain G aH set as shown in FIG. 12 , the lateral acceleration gain G 1H set as shown in FIG. 13 , and the vehicle speed gain G VH set as shown in FIG. 14 , as expressed in the following formula (5).
  • F 1 G ⁇ ⁇ G aH ⁇ G lH ⁇ G VH ⁇ F b 1
  • each of the accelerator position gain, the lateral acceleration gain and the vehicle speed gain is set using a corresponding one of the maps illustrated in FIGS. 15 to 17 which are different from those used in the situation where the high road surface friction mode is selected.
  • the accelerator position gain G aL is set such that it increases along with an increase in the accelerator position [%] to reach "1" at a second accelerator position value A 2 , and after the accelerator position becomes greater than the second accelerator position value A 2 , increases to a given value greater than "1".
  • the accelerator position gain G aL is set in this manner, the final instruction value for the vehicle attitude control becomes smaller along with a decrease in the accelerator position.
  • the second accelerator position value A 2 at which the accelerator position gain G aL in the low road surface friction mode becomes "1” is set to be greater than the first accelerator position value A 1 at which the accelerator position gain G aH in the high road surface friction mode becomes "1".
  • the second accelerator position value A 2 is set to about 60 to about 75 [%], and the accelerator position gain G aL is set such that it becomes equal to less than "1" in a range in which the acceleration position is equal to or less than this value, and becomes greater than "1" in a range in which the acceleration position is greater than this value.
  • the lateral acceleration gain G 1L is set such that it becomes zero in a range in which the lateral acceleration a 1 [G] is equal to or less than a second lateral acceleration value a 12 , and increases after the lateral acceleration becomes greater than the second lateral acceleration value a 12 , whereafter it converges to "1" after the lateral acceleration becomes equal to or greater than a given value.
  • the lateral acceleration gain different from that in the high road surface friction mode is set, so that, in the low and high road surface friction modes, different braking forces are generated with respect to the same lateral acceleration value.
  • the lateral acceleration gain G 1L in the above manner, in a range in which the lateral acceleration is equal to or less than the second lateral acceleration value a 12 , intervention of the vehicle attitude control is substantially avoided (as a result of multiplication by the lateral acceleration gain G 1L , the final instruction value for the vehicle attitude control becomes zero).
  • the second lateral acceleration value a 12 at which the lateral acceleration gain G 1L in the low road surface friction mode becomes greater than zero is set to be less than the first lateral acceleration value an.
  • the second lateral acceleration value a 12 is set to about 0.02 to about 0.15 [G]
  • the lateral acceleration gain G 1L is set such that it becomes zero in the range in which the lateral acceleration is equal to or less than this value.
  • the vehicle speed gain G VL is set such that it becomes zero in a range in which the vehicle speed is equal to or less than a second vehicle speed value V 2 , and increases after the vehicle speeds becomes greater than the second vehicle speed value V 2 , whereafter it converges to a given value less than "1" after the vehicle speed becomes equal to or greater than a given value.
  • the vehicle speed gain G VL is set in this manner, intervention of the vehicle attitude control is avoided in the range in which the vehicle speed is equal to or less than the second vehicle speed value V 2 , and the final instruction value for the vehicle attitude control is set to a relatively small value even in a high vehicle speed range. That is, in the situation where the low road surface friction mode is selected, intervention of the vehicle attitude control is suppressed in any vehicle speed range, as compared to the high road surface friction mode. In other words, it is intended to suppress a situation where slip occurs in the inner rear road wheel due to a braking force based on the vehicle attitude control.
  • the second vehicle speed value V 2 is set to about 15 to about 30 [km/h]
  • the vehicle speed gain G VL is set such that it converges to about 0.3 to about 0.6 in the high vehicle speed range.
  • the final instruction value F 1 for the vehicle attitude control is calculated by multiplying the basic instruction value F b1 for the vehicle attitude control by the steering angle gain G ⁇ set as shown in FIG. 11 , the accelerator position gain G aL set as shown in FIG. 15 , the lateral acceleration gain G 1L set as shown in FIG. 16 , and the vehicle speed gain G VL set as shown in FIG. 17 , as expressed in the following formula (6).
  • F 1 G ⁇ ⁇ G aL ⁇ G lL ⁇ G VL ⁇ F b 1
  • the rotation speed difference gain G DL is set such that it is kept at "1" when a difference in rotation speed between an inner road wheel and an outer road wheel is equal to or less than a first rotation speed difference value D 1 [m/sec], and converges to a given value greater than "1" when the rotation speed difference is greater than the first rotation speed difference value D 1 .
  • the final instruction value for the brake LSD control increases after the rotation speed difference becomes greater than the first rotation speed difference value D 1 .
  • a braking force to be applied to the inner road wheel when slip occurs in the inner road is set to a value greater than that in the situation where the high road surface friction mode is selected, thereby strongly suppressing slip of the inner road wheel.
  • the first rotation speed difference value D 1 is set to about 8 to about 12 [m/sec]
  • the final instruction value for the brake LSD control is set such that it increase in a range in which the rotation speed difference becomes greater than the first rotation speed difference value D 1 .
  • the rotation speed difference gain G DL is set such that it converges to about 1.3 to about 1.6 in a range in which the rotation speed difference D is large.
  • the final instruction value F 2 for the brake LSD control is calculated by multiplying the basic instruction value F b2 for the brake LSD control by the rotation speed difference gain G DL set as shown in FIG. 18 , as expressed in the following formula (7).
  • the rotation speed difference gain G DL is kept at "1"
  • the basic instruction value F b2 is directly used as the final instruction value F 2 .
  • F 2 G DL ⁇ F b 2
  • the final instruction value F 1 for the vehicle attitude control is calculated by the formula (5) or (6) based on the basic instruction value F b1 for the vehicle attitude control.
  • the final instruction value F 2 for the brake LSD control is calculated by the formula (7) based on the basic instruction value F b2 for the brake LSD control, or the basic instruction value F b2 is directly used as the final instruction value F 2 .
  • the final instruction value F 3 for the pre-brake LSD control is calculated by multiplying the basic instruction value F b3 for the pre-brake LSD control by the same gains as those used in the vehicle attitude control. That is, the final instruction value F 3 is calculated by the following formula (8).
  • the lower limit braking force based on the pre-brake LSD control is applied for the purpose of suppressing a change in braking force occurring in the period between completion of the application of the first braking force based on the vehicle attitude control and start of the application of the second braking force based on the brake LSD control.
  • the basic instruction value for the pre-brake LSD control is multiplied by the same gains as those used in the vehicle attitude control, thereby setting the lower limit braking force such that it is smoothly continuous with the first braking force based on the vehicle attitude control.
  • F 3 G ⁇ ⁇ G aL ⁇ G lL ⁇ G VL ⁇ F b 3
  • the vehicle attitude control system may be configured such that the pre-brake LSD control is executed even in the situation where the high road surface friction mode is selected.
  • the final instruction value F 3 may be calculated by the following formula (9). This makes it possible to set, in the high road surface friction mode, the lower limit braking force such that it is smoothly continuous with the first braking force based on the vehicle attitude control.
  • F 3 G ⁇ ⁇ G aH ⁇ G lH ⁇ G VH ⁇ F b 3
  • step S26 illustrated in FIG. 7 , current ones of the final instruction value F 1 for the vehicle attitude control, the final instruction value F 2 for the brake LSD control and the final instruction value F 3 for the pre-brake LSD control are compared with each other, and a largest one of the final instruction values is finally set as an instruction value of a braking force be applied to the inner rear road wheel.
  • the processing subroutine proceeds to the step S5 of the flowchart in FIG. 6 .
  • the brake unit 8 of the inner rear road wheel is controlled based on the set instruction value.
  • the vehicle attitude control system is configured to, during turning of the vehicle 1 based on turning manipulation of the steering wheel 6 of the vehicle 1 (the step 17 in FIG. 7 ), execute the vehicle attitude control of, based on the difference in road wheel speed between the inner rear road wheel and the outer rear road wheel of the vehicle 1 being turning, applying the first braking force (the step S20 in FIG. 7 ) to the inner rear road wheel.
  • a force acts on the vehicle body 1a through the suspension 3 to pull the inner rear portion of the vehicle body 1a downwardly, so that it is possible to suppress uplift of the inner rear portion of the vehicle body 1a.
  • the first braking force is applied to the inner rear road wheel based on the road wheel speed difference between the inner and outer rear road wheels, and, after the application of the first braking force, a braking force equal to or greater than the lower limit braking force is maintained until the turning is completed (after the time t 4 in FIG. 9 ), even when the road wheel speed difference becomes smaller, so that it is possible to suppress a situation where the braking force based on the vehicle attitude control sudden changes, thereby giving a driver a feeling of strangeness.
  • the second braking force is applied to the inner rear road wheel (the step S22 in FIG. 7 ), so that it is possible to suppress a rise in road wheel speed of the inner rear road wheel due to slip thereof, and suppress the slip of the inner rear road wheel.
  • the brake actuator is controlled to apply the largest braking force among the first braking force, the lower limit braking force, and the second braking force (the step S26 in FIG. 7 ), so that it is possible to suppress interference among controls for applying a braking force for respective different purposes.
  • the lower limit braking force is set, so that it is possible to suppress a situation where the lower limit braking force is applied in the high road surface friction mode in which the lower limit braking force is unnecessary, thereby giving a driver a feeling of strangeness.
  • the upper arm 3a and the lower arm 3b constituting the link mechanism suspending an axle portion of each of the rear road wheels 2c, 2d with respect to the vehicle body 1a suspends the axle portion 2e such that the axle portion is swingable about the given suspension center P S ( FIG. 4 ). Further, the suspension center is located above the axle portion 2e.
  • the vehicle attitude control system of the present invention has been applied to a rear drive vehicle
  • the vehicle attitude control system of the present invention may be applied to a vehicle having any other drive system, such as a 4-wheel drive vehicle.

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  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Automation & Control Theory (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Physics & Mathematics (AREA)
  • Mathematical Physics (AREA)
  • Regulating Braking Force (AREA)
  • Vehicle Body Suspensions (AREA)
EP20176232.5A 2019-06-04 2020-05-25 Vehicle attitude control system Withdrawn EP3747715A1 (en)

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Cited By (1)

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US20220176826A1 (en) * 2020-12-08 2022-06-09 Hyundai Motor Company Braking control method using predicted friction coefficient of brake pad

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JP7193784B2 (ja) * 2020-03-09 2022-12-21 トヨタ自動車株式会社 車両制御装置
KR20220045606A (ko) * 2020-10-05 2022-04-13 현대자동차주식회사 차량의 서스펜션 제어 장치 및 그 방법
CN114715269A (zh) * 2022-04-01 2022-07-08 北京汽车集团越野车有限公司 辅助转向的方法、电子设备、装置及具有该装置的车辆

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EP0618115A2 (en) * 1993-03-31 1994-10-05 Toyota Jidosha Kabushiki Kaisha Anti-lock/traction control brake system
DE19510104C1 (de) * 1995-03-20 1996-08-14 Bayerische Motoren Werke Ag ABS- und/oder ASC-Regelsystem für Kraftfahrzeuge
DE19522632A1 (de) * 1995-06-22 1997-01-02 Teves Gmbh Alfred Verfahren zur Verbesserung des Regelverhaltens eines Blockierschutzregelungssystems
EP0872393A2 (de) * 1997-04-16 1998-10-21 Volkswagen Aktiengesellschaft Verfahren zur Bremsdruckregelung eines Kraftfahrzeuges
EP0962370A2 (en) * 1998-06-01 1999-12-08 Delphi Technologies, Inc. Method for controlling vehicle behaviour during cornering and a braking system for implementation thereof
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US11827120B2 (en) * 2020-12-08 2023-11-28 Hyundai Motor Company Braking control method using predicted friction coefficient of brake pad

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